172 THE COTTON PLANT IN EGYPT CHAP. 



diameter, while the Egyptian boll was only 27 mm. in 

 diameter. On crossing the two strains we effectively 

 placed the Egyptian seed inside a boll whose cubic 

 capacity had been doubled, and an increase in seed-size 

 followed. Thus we may regard the Egyptian seed as 

 being constitutionally large, and dominant over the 

 genuinely small Upland seed. At gametogenesis in F l5 

 the two seed-weight allelomorphs separate from one 

 another, and the 3 : 1 ratio appears in F 2 if we clear 

 away the lumber brought in by autogenous fluctuation. 



We have discussed this masking of the difference in 

 seed-weight*, and the development of the difference under 

 equal opportunities, in terms of boll-width alone for 

 convenience, though other factors are also involved. The 

 displacement of the means for such dissected graphs, 

 when compared with the probable error of a pure strain, 

 which is obviously too stringent a test for these hetero- 

 geneous groups, gave significant deviations in respect of 

 " discontinuous growth " ; a slight but significant deviation 

 with respect to branching ; a slight indication of connec- 

 tion between extensive shedding and heavy seed, which 

 is probably indirect, since "discontinuous growth " sheds 

 less than the other types ; and a very marked relation 

 between wide or narrow boll and heavy or light seed 

 respectively. In the last case the figures were as follows : 



36 Widest bolls. Mean seed-weight + 9-4% (P.E x 3'2 == 4-3%) 

 24 Narrowest bolls. 13-2% (P.E X 3-2 = 5-3%) 



The simple cross of Sultani x Afifi showed dominance 

 of heavy seed over light in F a (Fig. 67), and although 

 the difference between the two parents was very small, 

 yet some indication of segregation is shown. This takes 

 the form of two modes in the F 2 curve, which appear in 

 both the brother families ; since the mean weights are 

 computed, and hence do not suffer from any subjective 

 error, this coincidence is probably significant, and due to 



